Mar 14-Fish I.docx

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School

McGill University

Department

Biology (Sci)

Course

BIOL 305

Professor

Virginie Millien

Semester

Winter

Description

14/03/14
Fish I
Vertebrates are not that diverse when compared with invertebrates
BUT we’re BIG. This is mainly due to the iodine fixing endostyle gland (or thyroid).
Within vertebrates, half are fish. Most fish are ray­finned fishes.
Agnathans:
­ Hagfish and Lamprey:
o parasitic or very derived, unspecialized for active predation. They live
more of a scavenging lifestyle
o They are basal. The dichotomy between jawless and jawed fishes seems to
be at the base of vertebrate phylogeny
­ From the base somehow came the hagfish and lamprey, but the transition forms
between basal and extant forms are missing
­ Agnathan fish in the fossil record are covered in bone with dentine and enamel on
the outside. The inside probably had cartilage for muscle attachment (as opposed
to arthropods which attach muscles to the outer skeleton)
o Eg. Osteostaci: Have paired fins, a propulsive tail and dorsal fins to
prevent yaw which suggests active swimming
Due to their aquatic environment, fish have to:
­ deal with drag,
­ produce thrust (best done from the back),
­ and overcome gravity (through active propulsion or by becoming neutrally
buoyant) because of their size and shape
General fish anatomy:
­ Sharks have a huge liver for neutral buoyancy and less for metabolism
­ Most sharks swim and use their pectoral fin’s angle to stay in the water column
­ Bony fish have swim bladders or lungs to remain neutrally buoyant and have
taken on a huge variety of anatomy
Origin of vertebrate head:
­ Neural crest cell is novel:
o From this one cell type develops most specialized anatomy in the head
th
(sometimes called the 4 cell type in the embryo)
 Neural crest cells develop into eyes, nose, ears, lateral line system,
peripheral nerves, many muscles, cranium (Most of the head,
except the brain)
­ Development of jaws and cranium:
o In early fishes, branchial skeleton of branchiostoma evolves in to
pharyngeal basket surrounded by cartilage called the splanchnocranium
(splanchno = gut). Head becomes centered around the sense organs
o Jawed fishes have modified the front two gill arches (arches of the
splanchtocranial pharynx) to create hinged jaws 14/03/14
 First arch becomes the jaw and second arch is a support for the
jaw. This allows for anterior/posterior mobile jaws (like in sharks)
o The jaw gets linked to neurocranium, and the rest of the splanchtocranium
are linked to the vertebral column.
o The outer dermatocranium covers the head: dermally derived bones
(extensions of plated armor that and the neurocranium is cartilage derived)
o Cranial nerves are segmented and related to a